This is an extract of the discussion between Andy Tanenbaum and Linus
Benedict Torvalds about kernel design, free software, and more. Only
contributions from the main actors are included. The complete
archive is also available, but only in BABYL format. You can use
Emacs RMAIL to read it conveniently.

I was in the U.S. for a couple of weeks, so I haven't commented much on
LINUX (not that I would have said much had I been around), but for what
it is worth, I have a couple of comments now.

As most of you know, for me MINIX is a hobby, something that I do in the
evening when I get bored writing books and there are no major wars,
revolutions, or senate hearings being televised live on CNN. My real
job is a professor and researcher in the area of operating systems.

As a result of my occupation, I think I know a bit about where operating
are going in the next decade or so. Two aspects stand out:

Most older operating systems are monolithic, that is, the whole operating
system is a single a.out file that runs in 'kernel mode.' This binary
contains the process management, memory management, file system and the
rest. Examples of such systems are UNIX, MS-DOS, VMS, MVS, OS/360,
MULTICS, and many more.

The alternative is a microkernel-based system, in which most of the OS
runs as separate processes, mostly outside the kernel. They communicate
by message passing. The kernel's job is to handle the message passing,
interrupt handling, low-level process management, and possibly the I/O.
Examples of this design are the RC4000, Amoeba, Chorus, Mach, and the
not-yet-released Windows/NT.

While I could go into a long story here about the relative merits of the
two designs, suffice it to say that among the people who actually design
operating systems, the debate is essentially over. Microkernels have won.
The only real argument for monolithic systems was performance, and there
is now enough evidence showing that microkernel systems can be just as
fast as monolithic systems (e.g., Rick Rashid has published papers comparing
Mach 3.0 to monolithic systems) that it is now all over but the shoutin`.

MINIX is a microkernel-based system. The file system and memory management
are separate processes, running outside the kernel. The I/O drivers are
also separate processes (in the kernel, but only because the brain-dead
nature of the Intel CPUs makes that difficult to do otherwise). LINUX is
a monolithic style system. This is a giant step back into the 1970s.
That is like taking an existing, working C program and rewriting it in
BASIC. To me, writing a monolithic system in 1991 is a truly poor idea.

Once upon a time there was the 4004 CPU. When it grew up it became an
8008. Then it underwent plastic surgery and became the 8080. It begat
the 8086, which begat the 8088, which begat the 80286, which begat the
80386, which begat the 80486, and so on unto the N-th generation. In
the meantime, RISC chips happened, and some of them are running at over
100 MIPS. Speeds of 200 MIPS and more are likely in the coming years.
These things are not going to suddenly vanish. What is going to happen
is that they will gradually take over from the 80x86 line. They will
run old MS-DOS programs by interpreting the 80386 in software. (I even
wrote my own IBM PC simulator in C, which you can get by FTP from
ftp.cs.vu.nl = 192.31.231.42 in dir minix/simulator.) I think it is a
gross error to design an OS for any specific architecture, since that is
not going to be around all that long.

MINIX was designed to be reasonably portable, and has been ported from the
Intel line to the 680x0 (Atari, Amiga, Macintosh), SPARC, and NS32016.
LINUX is tied fairly closely to the 80x86. Not the way to go.

Don`t get me wrong, I am not unhappy with LINUX. It will get all the people
who want to turn MINIX in BSD UNIX off my back. But in all honesty, I would
suggest that people who want a **MODERN** "free" OS look around for a
microkernel-based, portable OS, like maybe GNU or something like that.

Andy Tanenbaum (ast@cs.vu.nl)

P.S. Just as a random aside, Amoeba has a UNIX emulator (running in user
space), but it is far from complete. If there are any people who would
like to work on that, please let me know. To run Amoeba you need a few 386s,
one of which needs 16M, and all of which need the WD Ethernet card.

Well, with a subject like this, I'm afraid I'll have to reply.
Apologies to minix-users who have heard enough about linux anyway. I'd
like to be able to just "ignore the bait", but ... Time for some
serious flamefesting!

I was in the U.S. for a couple of weeks, so I haven't commented much on
LINUX (not that I would have said much had I been around), but for what
it is worth, I have a couple of comments now.

As most of you know, for me MINIX is a hobby, something that I do in the
evening when I get bored writing books and there are no major wars,
revolutions, or senate hearings being televised live on CNN. My real
job is a professor and researcher in the area of operating systems.

You use this as an excuse for the limitations of minix? Sorry, but you
loose: I've got more excuses than you have, and linux still beats the
pants of minix in almost all areas. Not to mention the fact that most
of the good code for PC minix seems to have been written by Bruce Evans.

Re 1: you doing minix as a hobby - look at who makes money off minix,
and who gives linux out for free. Then talk about hobbies. Make minix
freely available, and one of my biggest gripes with it will disappear.
Linux has very much been a hobby (but a serious one: the best type) for
me: I get no money for it, and it's not even part of any of my studies
in the university. I've done it all on my own time, and on my own
machine.

Re 2: your job is being a professor and researcher: That's one hell of a
good excuse for some of the brain-damages of minix. I can only hope (and
assume) that Amoeba doesn't suck like minix does.

1. MICROKERNEL VS MONOLITHIC SYSTEM

True, linux is monolithic, and I agree that microkernels are nicer. With
a less argumentative subject, I'd probably have agreed with most of what
you said. From a theoretical (and aesthetical) standpoint linux looses.
If the GNU kernel had been ready last spring, I'd not have bothered to
even start my project: the fact is that it wasn't and still isn't. Linux
wins heavily on points of being available now.

MINIX is a microkernel-based system. [deleted, but not so that you
miss the point ] LINUX is a monolithic style system.

If this was the only criterion for the "goodness" of a kernel, you'd be
right. What you don't mention is that minix doesn't do the micro-kernel
thing very well, and has problems with real multitasking (in the
kernel). If I had made an OS that had problems with a multithreading
filesystem, I wouldn't be so fast to condemn others: in fact, I'd do my
damndest to make others forget about the fiasco.

[ yes, I know there are multithreading hacks for minix, but they are
hacks, and bruce evans tells me there are lots of race conditions ]

2. PORTABILITY

"Portability is for people who cannot write new programs"
-me, right now (with tongue in cheek)

The fact is that linux is more portable than minix. What? I hear you
say. It's true - but not in the sense that ast means: I made linux as
conformant to standards as I knew how (without having any POSIX standard
in front of me). Porting things to linux is generally /much/ easier
than porting them to minix.

I agree that portability is a good thing: but only where it actually has
some meaning. There is no idea in trying to make an operating system
overly portable: adhering to a portable API is good enough. The very
/idea/ of an operating system is to use the hardware features, and hide
them behind a layer of high-level calls. That is exactly what linux
does: it just uses a bigger subset of the 386 features than other
kernels seem to do. Of course this makes the kernel proper unportable,
but it also makes for a /much/ simpler design. An acceptable trade-off,
and one that made linux possible in the first place.

I also agree that linux takes the non-portability to an extreme: I got
my 386 last January, and linux was partly a project to teach me about
it. Many things should have been done more portably if it would have
been a real project. I'm not making overly many excuses about it
though: it was a design decision, and last april when I started the
thing, I didn't think anybody would actually want to use it. I'm happy
to report I was wrong, and as my source is freely available, anybody is
free to try to port it, even though it won't be easy.

Linus

PS. I apologise for sometimes sounding too harsh: minix is nice enough
if you have nothing else. Amoeba might be nice if you have 5-10 spare
386's lying around, but I certainly don't. I don't usually get into
flames, but I'm touchy when it comes to linux :)

You use this [being a professor] as an excuse for the limitations of minix?

The limitations of MINIX relate at least partly to my being a professor:
An explicit design goal was to make it run on cheap hardware so students
could afford it. In particular, for years it ran on a regular 4.77 MHZ PC
with no hard disk. You could do everything here including modify and recompile
the system. Just for the record, as of about 1 year ago, there were two
versions, one for the PC (360K diskettes) and one for the 286/386 (1.2M).
The PC version was outselling the 286/386 version by 2 to 1. I don't have
figures, but my guess is that the fraction of the 60 million existing PCs that
are 386/486 machines as opposed to 8088/286/680x0 etc is small. Among students
it is even smaller. Making software free, but only for folks with enough money
to buy first class hardware is an interesting concept.
Of course 5 years from now that will be different, but 5 years from now
everyone will be running free GNU on their 200 MIPS, 64M SPARCstation-5.

Re 2: your job is being a professor and researcher: That's one hell of a
good excuse for some of the brain-damages of minix. I can only hope (and
assume) that Amoeba doesn't suck like minix does.

Amoeba was not designed to run on an 8088 with no hard disk.

If this was the only criterion for the "goodness" of a kernel, you'd be
right. What you don't mention is that minix doesn't do the micro-kernel
thing very well, and has problems with real multitasking (in the
kernel). If I had made an OS that had problems with a multithreading
filesystem, I wouldn't be so fast to condemn others: in fact, I'd do my
damndest to make others forget about the fiasco.

A multithreaded file system is only a performance hack. When there is only
one job active, the normal case on a small PC, it buys you nothing and adds
complexity to the code. On machines fast enough to support multiple users,
you probably have enough buffer cache to insure a hit cache hit rate, in
which case multithreading also buys you nothing. It is only a win when there
are multiple processes actually doing real disk I/O. Whether it is worth
making the system more complicated for this case is at least debatable.

I still maintain the point that designing a monolithic kernel in 1991 is
a fundamental error. Be thankful you are not my student. You would not
get a high grade for such a design :-)

The fact is that linux is more portable than minix. What? I hear you
say. It's true - but not in the sense that ast means: I made linux as
conformant to standards as I knew how (without having any POSIX standard
in front of me). Porting things to linux is generally /much/ easier
than porting them to minix.

MINIX was designed before POSIX, and is now being (slowly) POSIXized as
everyone who follows this newsgroup knows. Everyone agrees that user-level
standards are a good idea. As an aside, I congratulate you for being able
to write a POSIX-conformant system without having the POSIX standard in front
of you. I find it difficult enough after studying the standard at great length.

My point is that writing a new operating system that is closely tied to any
particular piece of hardware, especially a weird one like the Intel line,
is basically wrong. An OS itself should be easily portable to new hardware
platforms. When OS/360 was written in assembler for the IBM 360
25 years ago, they probably could be excused. When MS-DOS was written
specifically for the 8088 ten years ago, this was less than brilliant, as
IBM and Microsoft now only too painfully realize. Writing a new OS only for the
386 in 1991 gets you your second 'F' for this term. But if you do real well
on the final exam, you can still pass the course.

The limitations of MINIX relate at least partly to my being a professor:
An explicit design goal was to make it run on cheap hardware so students
could afford it.

All right: a real technical point, and one that made some of my comments
inexcusable. But at the same time you shoot yourself in the foot a bit:
now you admit that some of the errors of minix were that it was too
portable: including machines that weren't really designed to run unix.
That assumption lead to the fact that minix now cannot easily be
extended to have things like paging, even for machines that would
support it. Yes, minix is portable, but you can rewrite that as
"doesn't use any features", and still be right.

A multithreaded file system is only a performance hack.

Not true. It's a performance hack /on a microkernel/, but it's an
automatic feature when you write a monolithic kernel - one area where
microkernels don't work too well (as I pointed out in my personal mail
to ast). When writing a unix the "obsolete" way, you automatically get
a multithreaded kernel: every process does it's own job, and you don't
have to make ugly things like message queues to make it work
efficiently.

Besides, there are people who would consider "only a performance hack"
vital: unless you have a cray-3, I'd guess everybody gets tired of
waiting on the computer all the time. I know I did with minix (and yes,
I do with linux too, but it's /much/ better).

I still maintain the point that designing a monolithic kernel in 1991 is
a fundamental error. Be thankful you are not my student. You would not
get a high grade for such a design :-)

Well, I probably won't get too good grades even without you: I had an
argument (completely unrelated - not even pertaining to OS's) with the
person here at the university that teaches OS design. I wonder when
I'll learn :)

My point is that writing a new operating system that is closely tied to any
particular piece of hardware, especially a weird one like the Intel line,
is basically wrong.

But /my/ point is that the operating system /isn't/ tied to any
processor line: UNIX runs on most real processors in existence. Yes,
the /implementation/ is hardware-specific, but there's a HUGE
difference. You mention OS/360 and MS-DOG as examples of bad designs
as they were hardware-dependent, and I agree. But there's a big
difference between these and linux: linux API is portable (not due to my
clever design, but due to the fact that I decided to go for a fairly-
well-thought-out and tested OS: unix.)

If you write programs for linux today, you shouldn't have too many
surprises when you just recompile them for Hurd in the 21st century. As
has been noted (not only by me), the linux kernel is a miniscule part of
a complete system: Full sources for linux currently runs to about 200kB
compressed - full sources to a somewhat complete developement system is
at least 10MB compressed (and easily much, much more). And all of that
source is portable, except for this tiny kernel that you can (provably:
I did it) re-write totally from scratch in less than a year without
having /any/ prior knowledge.

In fact the /whole/ linux kernel is much smaller than the 386-dependent
things in mach: i386.tar.Z for the current version of mach is well over
800kB compressed (823391 bytes according to nic.funet.fi). Admittedly,
mach is "somewhat" bigger and has more features, but that should still
tell you something.

And reply I did, with complete abandon, and no thought for good taste
and netiquette. Apologies to ast, and thanks to John Nall for a friendy
"that's not how it's done"-letter. I over-reacted, and am now composing
a (much less acerbic) personal letter to ast. Hope nobody was turned
away from linux due to it being (a) possibly obsolete (I still think
that's not the case, although some of the criticisms are valid) and (b)
written by a hothead :-)

I've been getting a bit of mail lately from unhappy campers. (Actually 10
messages from the 43,000 readers may seem like a lot, but it is not really.)
There seem to be three sticking points:

Monolithic kernels are just as good as microkernels

Portability isn't so important

Software ought to be free

If people want to have a serious discussion of microkernels vs. monolithic
kernels, fine. We can do that in comp.os.research. But please don't sound off
if you have no idea of what you are talking about. I have helped design
and implement 3 operating systems, one monolithic and two micro, and have
studied many others in detail. Many of the arguments offered are nonstarters
(e.g., microkernels are no good because you can't do paging in user space--
except that Mach DOES do paging in user space).

If you don't know much about microkernels vs. monolithic kernels, there is
some useful information in a paper I coauthored with Fred Douglis, Frans
Kaashoek and John Ousterhout in the Dec. 1991 issue of COMPUTING SYSTEMS, the
USENIX journal). If you don't have that journal, you can FTP the paper from
ftp.cs.vu.nl (192.31.231.42) in directory amoeba/papers as comp_sys.tex.Z
(compressed TeX source) or comp_sys.ps.Z (compressed PostScript). The paper
gives actual performance measurements and supports Rick Rashid's
conclusion that microkernel based systems are just as efficient as
monolithic kernels.

As to portability, there is hardly any serious discussion possible any more.
UNIX has been ported to everything from PCs to Crays. Writing a portable
OS is not much harder than a nonportable one, and all systems should be
written with portability in mind these days. Surely Linus' OS professor
pointed this out. Making OS code portable is not something I invented
in 1987.

While most people can talk rationally about kernel design and portability,
the issue of free-ness is 100% emotional. You wouldn't believe how much
[expletive deleted] I have gotten lately about MINIX not being free. MINIX
costs $169, but the license allows making two backup copies, so the effective
price can be under $60. Furthermore, professors may make UNLIMITED copies
for their students. Coherent is $99. FSF charges >$100 for the tape
its "free" software comes on if you don't have Internet access, and I
have never heard anyone complain. 4.4 BSD is $800. I don't really
believe money is the issue. Besides, probably most of the people
reading this group already have
it.

A point which I don't think everyone appreciates is that making something
available by FTP is not necessarily the way to provide the widest distribution.
The Internet is still a highly elite group. Most computer users are NOT on it.
It is my understanding from PH that the country where MINIX is most widely used
is Germany, not the U.S., mostly because one of the (commercial) German
computer magazines has been actively pushing it. MINIX is also widely used in
Eastern Europe, Japan, Israel, South America, etc. Most of these people would
never have gotten it if there hadn't been a company selling it.

Getting back to what "free" means, what about free source code? Coherent
is binary only, but MINIX has source code, just as LINUX does. You can change
it any way you want, and post the changes here. People have been doing that
for 5 years without problems. I have been giving free updates for
years, too.

I think the real issue is something else. I've been repeatedly offered virtual
memory, paging, symbolic links, window systems, and all manner of features. I
have usually declined because I am still trying to keep the system simple
enough for students to understand. You can put all this stuff in your version,
but I won't put it in mine. I think it is this point which irks the people who
say "MINIX is not free," not the $60.

An interesting question is whether Linus is willing to let LINUX become "free"
of his control. May people modify it (ruin it?) and sell it? Remember the
hundreds of messages with subject "Re: Your software sold for money" when it
was discovered the MINIX Centre in England was selling diskettes with news
postings, more or less at cost?

Suppose Fred van Kempen returns from the dead and wants to take over, creating
Fred's LINUX and Linus' LINUX, both useful but different. Is that ok? The
test comes when a sizable group of people want to evolve LINUX in a way Linus
does not want. Until that actually happens the point is moot, however.

If you like Linus' philosophy rather than mine, by all means, follow him, but
please don't claim that you're doing this because LINUX is "free." Just
say that you want a system with lots of bells and whistles. Fine. Your choice.
I have no argument with that. Just tell the truth.

As an aside, for those folks who don't read news headers, Linus is in Finland
and I am in The Netherlands. Are we reaching a situation where another
critical industry, free software, that had been totally dominated by the U.S.
is being taken over by the foreign competition? Will we soon see
President Bush coming to Europe with Richard Stallman and Rick Rashid
in tow, demanding that Europe import more American free software?

While most people can talk rationally about kernel design and portability,
the issue of free-ness is 100% emotional. You wouldn't believe how much
[expletive deleted] I have gotten lately about MINIX not being free. MINIX
costs $169, but the license allows making two backup copies, so the effective
price can be under $60. Furthermore, professors may make UNLIMITED copies
for their students. Coherent is $99. FSF charges >$100 for the tape
its "free" software comes on if you don't have Internet access, and I
have never heard
anyone complain. 4.4 BSD is $800. I don't really believe money is the issue.
Besides, probably most of the people reading this group already have it.

The distribution cost is not the problem. As you've noted, nobody complains
about the FSF's distribution fee being too high. The problem, as I see it,
is that there is only one legal source for for the software for people that
simply want a working release. And from watching the minix group since
minix first became available, my impression is that nobody enjoys dealing
with PH for a whole host of reasons.

I think the real issue is something else. I've been repeatedly offered virtual
memory, paging, symbolic links, window systems, and all manner of features. I
have usually declined because I am still trying to keep the system simple
enough for students to understand. You can put all this stuff in your version,
but I won't put it in mine. I think it is this point which irks the people who
say "MINIX is not free," not the $60.

If PH was not granted a monopoly on distribution, it would have been possible
for all of the interested minix hackers to organize and set up a group that
was dedicated to producing enhanced-minix. This aim of this group could have
been to produce a single, supported version of minix with all of the commonly
requested enhancements. This would have allowed minix to evolve in much the
same way that gcc has evolved over the last few years. Sure there are variant
versions of gcc, but most of the really good enhancements, bug fixes, etc
are eventually folded back into a master source base that future distributions
derive from. Thus you would have been left in peace to continue your tight
control over the educational version of minix, and everyone else that wanted
more than an educational tool could put their energies into enhanced-minx.

The primary reason I've never gotten into using minix, after the initial
excitement of hearing about it's availability way back when, is that I have
no interest in trying to apply random patches from all over the place, sort
out the problems, and eventually end up with a system that does what I want
it to, but which I can't pass on to anyone else.

The
test comes when a sizable group of people want to evolve LINUX in a way Linus
does not want. Until that actually happens the point is moot, however.

Where is the sizeable group of people that want to evolve gcc in a way that
rms/FSF does not approve of?

Where is the sizeable group of people that want to evolve emacs in a way that
rms/FSF doesn't approve of?

I'd say that if the primary maintainers of a large piece of useful, freely
redistributable, software are at all responsive to incorporating useful
enhancements and acting as the central repository and clearing house for
the software, then these splinter groups simply do not have sufficient
motivation to form. Having a single source for the software, and having
the primary maintainer(s) be unresponsive to the desires of a large group
of users, is the catalyst that causes these sorts of pressures; not the
freedom of the software.

If PH was not granted a monopoly on distribution, it would have been possible
for all of the interested minix hackers to organize and set up a group that
was dedicated to producing enhanced-minix. This aim of this group could have
been to produce a single, supported version of minix with all of the commonly
requested enhancements. This would have allowed minix to evolve in much the
same way that gcc has evolved over the last few years.

This IS possible. If a group of people wants to do this, that is fine.
I think co-ordinating 1000 prima donnas living all over the world will be
as easy as herding cats, but there is no legal problem. When a new release
is ready, just make a diff listing against 1.5 and post it or make it FTPable.
While this will require some work on the part of the users to install it,
it isn't that much work. Besides, I have shell scripts to make the diffs
and install them. This is what Fred van Kempen was doing. What he did wrong
was insist on the right to publish the new version, rather than diffs against
the PH baseline. That cuts PH out of the loop, which, not surprisingly, they
weren't wild about. If people still want to do this, go ahead.

Of course, I am not necessarily going to put any of these changes in my version,
so there is some work keeping the official and enhanced ones in sync, but I
am willing to co-operate to minimize work. I did this for a long time with
Bruce Evans and Frans Meulenbroeks.

If Linus wants to keep control of the official version, and a group of eager
beavers want to go off in a different direction, the same problem arises.
I don't think the copyright issue is really the problem. The problem is
co-ordinating things. Projects like GNU, MINIX, or LINUX only hold together
if one person is in charge. During the 1970s, when structured programming
was introduced, Harlan Mills pointed out that the programming team should
be organized like a surgical team--one surgeon and his or her assistants,
not like a hog butchering team--give everybody an axe and let them
chop away.

Anyone who says you can have a lot of widely dispersed people hack away on
a complicated piece of code and avoid total anarchy has never managed a
software project.

Where is the sizeable group of people that want to evolve gcc in a way that
rms/FSF does not approve of?

A compiler is not something people have much emotional attachment to.
If the language to be compiled is a given (e.g., an ANSI standard),
there isn't much room for people to invent new features. An operating
system has unlimited opportunity for people to implement their own
favorite features.

If Linus wants to keep control of the official version, and a group of eager
beavers want to go off in a different direction, the same problem arises.

This is the second time I've seen this "accusation" from ast, who feels
pretty good about commenting on a kernel he probably haven't even seen.
Or at least he hasn't asked me, or even read alt.os.linux about this.
Just so that nobody takes his guess for the full thruth, here's my
standing on "keeping control", in 2 words (three?):

I won't.

The only control I've effectively been keeping on linux is that I know
it better than anybody else, and I've made my changes available to
ftp-sites etc. Those have become effectively official releases, and I
don't expect this to change for some time: not because I feel I have
some moral right to it, but because I haven't heard too many complaints,
and it will be a couple of months before I expect to find people who
have the same "feel" for what happens in the kernel. (Well, maybe
people are getting there: tytso certainly made some heavy changes even
to 0.10, and others have hacked it as well)

In fact I have sent out feelers about some "linux-kernel" mailing list
which would make the decisions about releases, as I expect I cannot
fully support all the features that will /have/ to be added: SCSI etc,
that I don't have the hardware for. The response has been non-existant:
people don't seem to be that eager to change yet. (well, one person
felt I should ask around for donations so that I could support it - and
if anybody has interesting hardware lying around, I'd be happy to accept
it :)

The only thing the copyright forbids (and I feel this is eminently
reasonable) is that other people start making money off it, and don't
make source available etc... This may not be a question of logic, but
I'd feel very bad if someone could just sell my work for money, when I
made it available expressly so that people could play around with a
personal project. I think most people see my point.

That aside, if Fred van Kempen wanted to make a super-linux, he's quite
wellcome. He won't be able to make much money on it (distribution fee
only), and I don't think it's that good an idea to split linux up, but I
wouldn't want to stop him even if the copyright let me.

I don't think the copyright issue is really the problem. The problem is
co-ordinating things. Projects like GNU, MINIX, or LINUX only hold together
if one person is in charge.

Yes, coordination is a big problem, and I don't think linux will move
away from me as "head surgeon" for some time, partly because most people
understand about these problems. But copyright /is/ an issue: if people
feel I do a bad job, they can do it themselves. Likewise with gcc. The
minix copyright, however, means that if someone feels he could make a
better minix, he either has to make patches (which aren't that great
whatever you say about them) or start off from scratch (and be attacked
because you have other ideals).

Patches aren't much fun to distribute: I haven't made cdiffs for a
single version of linux yet (I expect this to change: soon the patches
will be so much smaller than the kernel that making both patches and a
complete version available is a good idea - note that I'd still make the
whole version available too). Patches upon patches are simply
impractical, especially for people that may do changes themselves.

Where is the sizeable group of people that want to evolve gcc in a way that
rms/FSF does not approve of?

A compiler is not something people have much emotional attachment to. If
the language to be compiled is a given (e.g., an ANSI standard), there isn't
much room for people to invent new features. An operating system has unlimited
opportunity for people to implement their own favorite features.